This invention relates to a combined board construction for burn-in and a burn-in equipment for use with the combined board to carry out burn-in for quality control and elimination of latent defects of semiconductor elements (herein after called "the devices") such as integrated circuit elements etc.
The burn-in is usually carried out in a temperature chamber exposing the devices in a high temperature atmosphere to provide a large stress to them and to reduce time for the burn-in by increasing acceleration factors.
As shown in FIG. 11(a) and 11(b) a burn-in board 1' with large number of I C sockets 2' on which the devices are to be mounted is displaced in a test room 100 in the temperature chamber to expose the devices to the high temperature atmosphere. On the other hand, a driver board 4' which generates signals to operate the devices is displaced outside 200 of the temperature chamber.
The burn-in board 1' and the driver board 4' are connected electrically through an edge 1' provided at the end of the burn-in board, an edge connector 64' installed in multistage or multistage and multi-rows on a surface of a thermally insulated wall 63, a feed through board 65' connected at the opposite end of the edge connector 64' passing through the wall 63, and a relay connector 66'. Thus, electric power and operating signals are supplied to the devices mounted on the I C socket 2' from the driver board 4' through the burn-in board 1'.
As operating speed of the devices is steadily increasing recently, high speed driving signals matching to the operate ink speed of the devices must be applied. In addition, as integration of the devices increases, increased time is required for activating all the cells in the devices, resulting in possible prolonged burn-in time. In the conventional equipment mentioned above, the long series connection of the burn-in board 1' and the driver board 4' requires longer circuit lines and delays the signal transmission. The conventional equipment, therefore, is not suitable for transmission of high speed signals.
Further, as the devices on the burn-in board are located at different distances from the edge, it is inevitable for each device to have a connecting circuit of different length. As a result, for high speed driving signaling, when the device located remotest from the edge connector 64' receives a signal pulse, the device nearest to the edge connector will be applied with next signal pulse, thus causing such problems as the impossibility of activating all the devices on the burn-in board at the same time. In addition, the connecting circuit, as it becomes longer, have caused such hindrance as distorted pulses etc. due to electrostatic capacity and resistance.
The problem and hindrance mentioned above can be solved to a certain degree, if the driver board, the feed-through board and the burn-in board are shortened. However, there is a limitation for this shortening, and the problem of different length of connecting circuit between the edge connector and each device on the burn-in board still remains unsettled.
On the other hand, the burn-in sometimes uses a test burn-in process which observes action of the devices in operation by a driver/test board. In this process, as signals go and return between tile devices and a measuring circuit, it requires more time for signals transmission and causes a larger difference of acting time between the devices.
In addition to the electric power and operating signals, many electrical connections for the measuring circuit are required and there are insufficient terminals at the edge connector. To cope with this, the operating circuit and the measuring circuit have been commonly used in parallel connection to plural devices. This has resulted in a large limitation on the numbers of measuring items and measuring speed, thus decreasing the measuring accuracy.
To solve the problems mentioned above,an equipment which has shortened signal circuit by placing a signal generating board in a temperature chamber has been proposed (Refer to Japanese Patent Laid Open Hei 5 - 19012). This equipment, however, cannot fully solve the above problems since the connecting circuit is not fully shortened. Further, no measures have been taken to eliminate the difference of connecting circuit length in each device.
Another type equipment is proposed in which burn-in and testing can be easily switched over by such a configuration that a burn-in board itself is made of a combination of an IC fitting board and a printed circuit board with edge terminals, where the detachable IC fitting board can be easily connected to a testing board outside a temperature chamber ( Refer to Japanese Patent Laid Open Hei 2 -190774). In this combination, however, though there is no explanation, the printed circuit board must be connected to the driver board which will be placed outside the temperature chamber when carrying out the burn-in. Therefore, this prior art hardly contributes to solve the above problems.